Method of producing support for planographic printing plate

ABSTRACT

Disclosed are (i) a method of producing a support for planographic printing plate, which comprises melting an aluminum ingot having an aluminum content of not less than 99.7 wt % to prepare a cast ingot, scalping the surface of the cast ingot, soaking the scalped cast ingot, cold rolling the soaked ingot to a thickness of 0.1 to 0.5 mm, correction of the resulting sheet to prepare an aluminum support, and then graining the aluminum support and (ii) a method of producing a support for planographic printing plate, which comprises melting an aluminum ingot having an aluminum content of not less than 99.7 wt % to prepare a cast ingot in a melt holding furnace, directly subjecting the cast ingot to continuous casting to prepare a thin sheet having a thickness of 2 to 30 mm, cold rolling the thin sheet, correction of the resulting sheet to prepare an aluminum support, and then graining the aluminum support.

FIELD OF THE INVENTION

The present invention relates to a method of producing a support forplanographic printing plate and more particularly relates to a method ofproducing an aluminum support which is superior in an electrolyticallygraining property.

BACKGROUND OF THE INVENTION

As an aluminum support for printing plate, particularly for offsetprinting plate there is used an aluminum plate (including aluminum alloyplate).

In general, an aluminum plate to be used as a support for offsetprinting plate needs to have a proper adhesion to a photographiclight-sensitive material and a proper water retention.

The surface of the aluminum plate should be uniformly and finely grainedto meet the aforesaid requirements. This graining process largelyaffects a printing performance and a durability of the printing plateupon the printing process following manufacture of the plate. Thus, itis important for the manufacture of the plate whether such graining issatisfactory or not.

In general, an alternating current electrolytic graining method is usedas the method of graining an aluminum support for a printing plate.There are a variety of suitable alternating currents, for example, anormal alternating waveform such as a sinewaveform, a specialalternating waveform such as a squarewaveform, and the like. When thealuminum support is grained by alternating current supplied between thealuminum plate and an opposite electrode such as a graphite electrode,this graining is usually conducted only one time, as the result ofwhich, the depth of pits formed by the graining is small over the wholesurface thereof. Also, the durability of the grained printing plateduring printing will deteriorate. Therefore, in order to obtain auniformly and closely grained aluminum plate satisfying the requirementof a printing plate with deep pits as compared with their diameters, avariety of methods have been proposed as follows.

One method is a graining method to use a current of particular waveformfor an electrolytic power source (JP-A-53-67507). (The term "JP-A" asused herein means an "unexamined published Japanese patentapplication".) Another method is to control a ratio between anelectricity quantity of a positive period and that of a negative periodat the time of alternating electrolytic graining (JP-A-54-65607). Stillanother method is to control the waveform supplied from an electrolyticpower source (JP-A-55-25381). Finally, another method is directed to acombination of current density (JP-A-56-29699).

Further, known is a graining method using a combination of an ACelectrolytic etching method with a mechanical graining method(JP-A-55-142695).

As the method of producing an aluminum support, on the other hand, knownis a method in which an aluminum ingot is melted and held, and then castinto a slab (having a thickness in a range from 400 to 600 mm, a widthin a range from 1,000 to 2,000 mm, and a length in a range from 2,000 to6,000 mm). Then, the cast slab thus obtained is subjected to a scalpingstep in which the slab surface is scalped by 3 to 10 mm with a scalpingmachine so as to remove an impurity structure portion on the surface.Next, the slab is subjected to a soaking treatment step in which theslab is kept in a soaking furnace at a temperature in a range from 480°to 540° C. for a time in a range from 6 to 12 hours, thereby to removeany stress inside the slab and make the structure of the slab uniform.Then, the thus treated slab is hot rolled at a temperature in a rangefrom 480° to 540° C. to a thickness in a range from 5 to 40 mm.Thereafter, the hot rolled slab is cold rolled at room temperature intoa plate of a predetermined thickness. Then, in order to make thestructure uniform and improve the flatness of the plate, the thus coldrolled plate is annealed thereby to make the rolled structure, etc.uniform, and the plate is then subjected to correction by cold rollingto a predetermined thickness. Such an aluminum plate obtained in themanner described above has been used as a support for a planographicprinting plate.

However, electrolytic graining is apt to be influenced by an aluminumsupport to be treated. If an aluminum support is prepared throughmelting and holding, casting, scalping and soaking, even though passingthrough repetition of heating and cooling followed by scalping of asurface layer, scattering of the metal alloy components is generated inthe surface layer, causing a drop in the yield of a planographicprinting plate.

In this connection, the present inventors have previously proposed amethod of producing a support for planographic printing plate, whichcomprises continuously performing casting and hot-rolling from moltenaluminum to form a hot-rolled coil of a thin plate, transforming thehot-rolled coil into an aluminum support through cold-rolling,heat-treatment and correction, and finally, graining the aluminumsupport (U.S. Pat. No. 5,078,805 which corresponds to JP-A-3-79798).

However, even the preparation methods which have been previouslyproposed by the present inventors give the non-uniformity of the yieldof electrolytic graining and the graining property due to the componentsof aluminum support.

Further, in order to prepare an aluminum alloy having the foregoingcomposition, a method is normally employed which comprises melting aningot having an aluminum content of not less than 99.7%, and then addingan aluminum mother alloy containing predetermined amounts of Fe, Si andCu to the molten aluminum. This aluminum mother alloy is expensive ascompared with an aluminum ingot, raising the cost of aluminum alloy.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method of producing asupport for planographic printing plate which is superior in grainingproperty and which reduces the non-uniformity in quality of materialsfor aluminum support, thereby improving the yield of electrolyticgraining as well as enabling the production of a low cost planographicprinting plate.

The present inventors have made extensive studies on the relationshipbetween aluminum support and electrolytic graining. As a result, thepresent inventors worked out the present invention.

In particular, the foregoing object of the present invention isaccomplished with:

(i) a method of producing a support for planographic printing plate,which comprises melting an aluminum ingot having an aluminum content ofnot less than 99.7 wt % to prepare a cast ingot, scalping the surface ofthe cast ingot, soaking the scalped cast ingot, cold rolling the soakedingot to a thickness of 0.1 to 0.5 mm, without followed by annealing,correction of the resulting sheet to prepare an aluminum support, andthen graining the aluminum support; and

(ii) a method of producing a support for planographic printing plate,which comprises melting an aluminum ingot having an aluminum content ofnot less than 99.7 wt % to prepare a cast ingot in a melt holdingfurnace, directly subjecting the cast ingot to continuous casting toprepare a thin sheet having a thickness of 2 to 30 mm, cold rolling thethin sheet, without followed by annealing, correction of the resultingsheet to prepare an aluminum support, and then graining the aluminumsupport.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1(A) and 1(B) illustrate the concept of an embodiment of thecasting process in the method of producing a support for planographicprinting plate according to the present invention, in which 1 indicatesa casting mold, 2 and 6 indicate a cast ingot, 3 indicates awater-cooled casting mold, 4 indicates a cast ingot receiving tray, and5 indicates a molten aluminum supplying nozzle.

FIG. 2 illustrates the concept of another embodiment of the castingprocess in the method of producing a support for planographic printingplate according to the present invention, in which 7 indicates a meltholding furnace, 8 indicates a twin-roller continuous casting machine,and 9 indicates a coiler.

FIG. 3 illustrates the concept of an embodiment of the cold rollingprocess in the method of producing a support for planographic printingplate according to the present invention, in which 10 indicates a coldrolling machine.

FIG. 4 illustrates the concept of an embodiment of the correctionprocess in the method of producing a support for planographic printingplate according to the present invention, in which 11 indicates acorrection machine.

FIG. 5 illustrates the concept of an embodiment of the heat treatmentprocess for intermediate annealing in a conventional method of producinga support for planographic printing plate, in which 12 represents a heattreatment furnace for intermediate annealing.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention, as the method for preparing an aluminum castingot from molten aluminum in, e.g., a fixed casting mold, a castingtechnique such as DC method has been put into practical use.

Further, as a continuous casting method employing a driven casting moldthere can be used a method employing a cooling belt such as Hapelettmethod or a method employing a cooling roller such as Hunter method and3C method. Moreover, JP-A-60-238001, JP-A-60-240360, etc. disclose amethod for preparing a coil of thin sheet.

According to conventional methods, when a support for printing plate isprepared only from an aluminum ingot having an aluminum content of notless than 99.7 wt %, it is disadvantageous in that the shape of grain iscollapsed during electrolytic graining. The present invention provides amethod of producing a support for planographic printing plate having agood adaptability to electrolytic graining by correction without heattreatment after cold rolling.

Referring to FIGS. 1(A), 1(B), 2, 3 and 4, an embodiment of the methodof producing an aluminum support according to the present invention willbe further described. As shown in FIG. 1(A), the reference number 1 is acasting mold in which an ingot is formed into cast ingot 2.Alternatively, as shown in FIG. 1(B), molten aluminum may be suppliedinto cast ingot receiving tray 4 from molten aluminum supplying nozzle 5through water-cooled casting mold 3 to prepare cast ingot 6. Further, asshown in FIG. 2, an aluminum ingot may be melted in melt holding furnace7, and then formed into a sheet having a thickness of 2 to 30 mm bymeans of twin-roller continuous casting machine 8. In a case of using acast ingot, it is scalped to a certain extent, soaked, cold rolled to athickness of 0.1 to 0.5 mm as shown in FIG. 3, and then corrected asshown in FIG. 4 to prepare an aluminum support. In this process, soakingis effected before cold rolling. In the case where an aluminum ingot ismelted in melt holding furnace 7 and formed into a sheet having athickness of about 4 to 30 mm by twin-roller continuous casting machine8, the sheet is then cold rolled by cold rolling machine 10 as shown inFIG. 3, and then, without followed by annealing, correction bycorrection machine 11 as shown in FIG. 4 to prepare a support.

The feature of the present invention is that no annealing treatment iseffected after cold rolling.

In the present invention, the soaking treatment is conducted at atemperature of 280° to 650° C., preferably 400° to 630° C., morepreferably 500° to 600° C. for a period of 2 to 15 hours, preferably 4to 12 hours, more preferably 6 to 11 hours.

In the present invention, while a variety of known continuous castingmethods is applicable, preferred are a twin-roller continuous castingmethod and a twin-belt continuous casting method. In a case of using thetwin-roller continuous casting method, it is preferred that a cast ingotis cast to a thin sheet having a thickness of 2 to 10 mm. In a case ofusing the twin-belt continuous casting method, it is preferred that acast ingot is cast to a sheet having a thickness of 10 to 30 mm,subsequently the sheet is hot rolled to a thickness of 2 to 10 mm(before cold rolling).

As the method for graining the support for planographic printing plateaccording to the present invention, there is used mechanical graining,chemical graining, electrochemical graining or combination thereof.

Examples of mechanical graining methods include ball graining, wiregraining, brush graining, and liquid honing. As electrochemical grainingmethod, there is normally used AC electrolytic etching method. Aselectric current, there is used a normal alternating current such assinewaveform or a special alternating current such as squarewaveform,and the like. As a pretreatment for the electrochemical graining,etching may be conducted with caustic soda.

If electrochemical graining is conducted, it is preferably with analternating current in an aqueous solution mainly composed ofhydrochloric acid or nitric acid. The electrochemical graining will befurther described hereinafter.

First, the aluminum is etched with an alkali. Preferred examples ofalkaline agents include caustic soda, caustic potash, sodiummetasilicate, sodium carbonate, sodium aluminate, and sodium gluconate.The concentration of the alkaline agent, the temperature of the alkalineagent and the etching time are preferably selected from 0.01 to 20%, 20°to 90° C. and 5 sec. to 5 min., respectively. The preferred etching rateis in the range of 0.1 to 5 g/m².

In particular, if the support contains a large amount of impurities, theetching rate is preferably in the range of 0.01 to 1 g/m²(JP-A-1-237197). Since alkaline-insoluble substances (smut) are left onthe surface of the aluminum plate thus alkali-etched, the aluminum platemay be subsequently desmutted as necessary.

The pretreatment is effected as mentioned above. In the presentinvention, the aluminum plate is subsequently subjected to ACelectrolytic etching in an electrolyte mainly composed of hydrochloricacid or nitric acid. The frequency of the AC electrolytic current is inthe range of 0.1 to 100 Hz, preferably 0.1 to 1.0 Hz or 10 to 60 Hz.

The concentration of the etching solution is in the range of 3 to 150g/l, preferably 5 to 50 g/l. The solubility of aluminum in the etchingbath is preferably in the range of not more than 50 g/l, more preferably2 to 20 g/l. The etching bath may contain additives as necessary.However, in mass production, it is difficult to control theconcentration of such an etching bath.

The electric current density in the etching bath is preferably in therange of 5 to 100 A/dm², more preferably 10 to 80 A/dm². The waveform ofelectric current can be properly selected depending on the requiredquality and the components of aluminum support used but may bepreferably a special alternating waveform as described in JP-B-56-19280and JP-B-55-19191. (The term "JP-B" as used herein means an "examinedJapanese patent publication"). The waveform of electric current and theliquid conditions are properly selected depending on requiredelectricity as well as required quality and components of aluminumsupport used.

The aluminum plate which has been subjected to electrolytic graining isthen subjected to dipping in an alkaline solution as a part ofdesmutting treatment to dissolve smutts away. As such an alkaline agent,there may be used caustic soda or the like. The desmutting treatment ispreferably effected at a pH value of not lower than 10 and a temperatureof 25° to 60° C. for a dipping time as extremely short as 1 to 10seconds.

The aluminum plate thus etched is then dipped in a solution mainlycomposed of sulfuric acid. It is preferred that the sulfuric acidsolution is in the concentration range of 50 to 400 g/l, which is muchlower than the conventional value, and the temperature range of 25° to65° C. If the concentration of sulfuric acid is more than 400 g/l or thetemperature of sulfuric acid is more than 65° C., the processing bath ismore liable to corrosion, and in an aluminum alloy comprising not lessthan 0.3% of manganese, the grains formed by the electrochemicalgraining is collapsed. Further, if the aluminum plate is etched by morethan 0.2 g/m², the printing durability reduces. Thus, the etching rateis preferably controlled to not more than 0.2 g/m².

The aluminum plate preferably forms an anodized film thereon in anamount of 0.1 to 10 g/m², more preferably 0.3 to 5 g/m².

The anodizing conditions vary with the electrolyte used and thus are notspecifically determined. In general, it is appropriate that theelectrolyte concentration is in the range of 1 to 80% by weight, theelectrolyte temperature is in the range of 5° to 70° C., the electriccurrent density is in the range of 0.5 to 60 A/dm², the voltage is inthe range of 1 to 100 V, and the electrolysis time is in the range of 1second to 5 minutes.

The grained aluminum plate having an anodized film thus obtained isstable and excellent in hydrophilicity itself and thus can directly forma photosensitive coat thereon. If necessary, the aluminum plate may befurther subjected to surface treatment.

For example, a silicate layer formed by the foregoing metasilicate ofalkaline metal or an undercoating layer formed by a hydrophilicpolymeric compound may be formed on the aluminum plate. The coatingamount of the undercoating layer is preferably in the range of 5 to 150mg/m².

A photosensitive coat is then formed on the aluminum plate thus treated.The photosensitive printing plate is imagewise exposed to light, andthen developed to make a printing plate, which is then mounted in aprinting machine for printing.

The present invention will be further described in the followingnon-limiting examples. Unless otherwise indicated, all parts, percents,ratios and the like are by weight.

EXAMPLE 1

A commercially available ingot having an aluminum content of not lessthan 99.7% (including 0.085% of Fe, 0.034% of Si and almost 0 (zero) %of Cu as impurities) was melted, and then formed into a cast ingot in acarbon casting mold at a casting temperature of 750° C. as shown in FIG.1(A). The cast ingot was scalped by about 10 mm, subjected to soaking ata temperature of 550° C. for 10 hours, and then finished to a thicknessof 0.24 mm only by cold rolling to prepare a sample of Example 1 of thepresent invention.

COMPARATIVE EXAMPLES 1 AND 2

In order to prepare a JIS1050 material that can be widely used as asupport for planographic printing plate, various mother alloys wereadded to a commercially available ingot to make a composition consistingof 0.35% of Fe, 0.07% of Si, 0.01% of Cu, 0.03% of Ti, and a balance ofAl and unavoidable impurities. The ingot was then formed into a castingot in the same manner as in Example 1. The cast ingot was scalped byan ordinary method, subjected to soaking, subjected to cold rolling andintermediate annealing (using an apparatus as shown in FIG. 5) once ormore times, and then cold rolled again so that it was finished to athickness of 0.24 mm to prepare a sample of Comparative Example 1.

As another comparative example, a cast ingot was prepared from an ingothaving an aluminum content of 99.7%. The cast ingot was then finished toa thickness of 0.24 mm in the same manner as in Comparative Example 1 toprepare a sample of Comparative Example 2.

The aluminum plates thus prepared were used as supports for planographicprinting plate. These supports were etched with a 15% aqueous solutionof caustic soda at a temperature of 50° C. at an etching rate of 5 g/m²,washed with water, desmutted with a 150 g/l sulfuric acid at atemperature of 50° C. for 10 seconds, and then washed with water.

These supports were then subjected to electrochemical graining with analternating current as described in JP-B-55-19191 in a 16 g/l nitricacid. The electrolysis conditions were 14 V for anode voltage V_(A), 12V for cathode voltage V_(c), and 350 coulomb/dm² for anodic electricity.

Without coating a photosensitive layer, the substrates 1 to 3 thusprepared were then evaluated for uniformity in appearance and grainshape (evaluated by observing a view of grained surface enlarged by ascanning electron microscope). At the same time, the cost of the rawmaterials of these substrates were compared. The results are set forthin Table 1.

                  TABLE 1                                                         ______________________________________                                                                              Cost                                                         Uniformity       ratio                                               Rolling  in        Grain  of raw                                  Component   method   appearance                                                                              shape  materials                               ______________________________________                                        Ex. 1:                                                                              Al, 99.7% Cold     Good    Good   100                                                   rolling                                                       C.Ex. JIS1050   Cold     Streak  Good   106                                   1:              rolling  unevenness                                                           + Inter-                                                                      mediate                                                                       annealing                                                     C.Ex. Al, 99.7% Cold     Streak  Melted,                                                                              100                                   2:              rolling  unevenness                                                                            poor                                                         + Inter-                                                                      mediate                                                                       annealing                                                     ______________________________________                                    

As mentioned above, the example of the present invention exhibits a goodappearance and grain shape and an excellent adaptability to graining.Further, the example of the present invention has a great effect ofreducing the cost of raw materials. In accordance with the presentinvention, a planographic printing plate can be prepared only from acommercially available ingot having an aluminum content of not less than99.7%, thereby enabling a drastic cost reduction.

Moreover, the present invention can employ a simplified rolling method,enabling a production cost reduction.

While casting is effected with a carbon casting mold in Example 1, thepresent invention is not limited thereto. Twin-roller continuous castingmethod as shown in FIG. 2 and twin-belt continuous casting method can beused to accomplish the same effects as above.

EXAMPLE 2

Referring to FIG. 2 which illustrates the concept of a casting process,another embodiment of the process for producing an aluminum support tobe used in the present invention will be described below.

An aluminum ingot having an aluminum content of not less than 99.7%(including 0.085% of Fe, 0.034% of Si, and almost 0 (zero) % of Cu asimpurities) was melted in melt holding furnace 7, and then continuouslycasted into a sheet having a thickness of 7 mm by twin-roller continuouscasting machine 8. The sheet was wound on coiler 9, and thensubsequently subjected to treatment by cold rolling machine 10 andcorrection machine 11 as shown in FIGS. 3 and 4, respectively, toprepare an aluminum support as a sample of Example 2 of the presentinvention.

COMPARATIVE EXAMPLE 3

An aluminum ingot having an aluminum content of not less than 99.7% wasmelted and held with a mother alloy of Fe, Si, Cu and Ti being addedthereto so that a composition comprising 0.35% of Fe, 0.07% of Si, 0.01%of Cu and 0.03% of Ti was made. The cast ingot thus prepared was thencasted in the same manner as in Example 2 to prepare an aluminum supportas a sample of Comparative Example 3.

These samples were then subjected to graining in the same manner as inExample 1 and Comparative Examples 1 and 2, anodized by an ordinarymethod, and then coated with a photosensitive layer to preparephotosensitive planographic printing plates. These photosensitiveplanographic printing plates were exposed to light, developed, and thengummed to prepare planographic printing plates. These planographicprinting plates were then used for printing in an ordinary manner. Theresults of the printing properties as well as the results of uniformityin appearance after graining and the comparison of the cost of rawmaterials are set forth in Table 2.

                  TABLE 2                                                         ______________________________________                                                           Results   Uniformity                                                                            Cost ratio                               Com-       Rolling of        in      of-raw                                   ponent     method  printing  appearance                                                                            materials                                ______________________________________                                        Ex. 2:                                                                              Al,      Cold    Good    Good    100                                          99.7%    rolling                                                        C.Ex. JIS1050  Cold    Acceptable                                                                            Poor    106                                    3:             rolling                                                        ______________________________________                                    

As mentioned above, the sample of the present invention can provideimproved results of printing, a drastically improved appearance and areduction of the cost of raw materials.

As mentioned above, the planographic printing plate prepared accordingto the method of producing a support for planographic printing plate ofthe present invention exhibits an improved adaptability to electrolyticgraining as compared with conventional planographic printing plates,thereby enabling a drastic reduction of the cost of raw materials.Further, the present invention eliminates the necessity of blending ofraw materials with a mother alloy, eliminating the drop of yield due toblending and hence enhancing the yield.

Moreover, the simplification of cold rolling process gives a greateffect of reducing the production cost, providing a great contributionto the quality improvement and cost reduction of support forplanographic printing plate.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one of ordinaryskill in the art that various changes and modifications can be madetherein without departing from the spirit and scope thereof.

What is claimed is:
 1. A method of producing a support for planographicprinting plate, which consists essentially of melting an aluminum ingothaving an aluminum content of not less than 99.7 wt % to prepare a castingot, scalping the surface of the cast ingot, soaking the scalped castingot, cold rolling the soaked ingot to a thickness of 0.1 to 0.5 mm,correction of the resulting sheet to prepare an aluminum support, andthen graining the aluminum support.
 2. A method of producing a supportfor planographic printing plate, which consists essentially of meltingan aluminum ingot having an aluminum content of not less than 99.7 wt %to prepare a cast ingot in a melt holding furnace, directly subjectingthe cast ingot to continuous casting to prepare a thin sheet having athickness of 2 to 30 mm, cold rolling the thin sheet, correction of theresulting sheet to prepare an aluminum support, and then graining thealuminum support.
 3. A method of producing a support for planographicprinting plate as claimed in claim 2, which consists essentially ofmelting an aluminum ingot having an aluminum content of not less than99.7 wt % to prepare a cast ingot in a melt holding furnace, directlysubjecting the cast ingot to twin-roller continuous casting to prepare athin sheet having a thickness of 2 to 10 mm, cold rolling the sheet,correction of the resulting sheet to prepare an aluminum support, andthen graining the aluminum support.
 4. A method of producing a supportfor planographic printing plate as claimed in claim 2, which consistsessentially of melting an aluminum ingot having an aluminum content ofnot less than 99.7 wt % to prepare a cast ingot in a melt holdingfurnace, directly subjecting the cast ingot to twin-belt continuouscasting to prepare a thin sheet having a thickness of 10 to 30 mm, hotrolling the sheet having a thickness of 2 to 10 mm, cold rolling thesheet, correction of the resulting sheet to prepare an aluminum support,and then graining the aluminum support.